1. Field of the Invention
The present invention relates to an apparatus, method and program for detecting a pointer position in the video-frame image that is projected by an overhead projector (OHP) during a lecture. The invention also relates to an apparatus, method and program for associating images, which can associate an OHP file used in, for example, a lecture with a moving image and can clearly indicate any region of an OHP-projected image, pointed during the lecture, on the OHP file. Further, the invention relates to a content-distributing server that can distribute contents thus prepared.
2. Description of the Related Art
E-learning is now being employed in the in-house education and general education. E-learning is a remote-place education method that uses the Internet. In most cases, it utilizes the WEB screen. E-learning is available in various types. The type that accomplishes ordinary lectures most well playbacks moving pictures (video images) and displays magnified OHP contents in synchronism with the playback of moving pictures. Seeing the OHP contents thus displayed, the students can easily understand the OHP contents. That is, the OHP-pointer and the content of whatever pointed can be displayed at the same time. This can provide an environment that is almost identical to the real lecture in the classroom.
To realize this system it is required that the OHP content displayed be synchronized with the moving picture that explains the OHP. The OHP content is manually synchronized with the moving picture, in the existing authoring system for preparing E-learning contents. Inevitably, it takes a very long time to prepare the contents. To solve this problem, the inventors hereof have proposed a system called “system for associating moving pictures with source documents” (Japanese Patent Application No. 2002-080500). This system automatically associates moving pictures with the source documents.
In any real lecture, the lecturer explains OHP contents one after another. The OHP pointer moves on the screen as the lecturer explains the OHP contents. In the case of the E-learning content of picture-content synchronization type, only the OHP switching in the moving picture is detected, thereby switching the OHP display. This cannot enable the lecturer to call the students' attention to that part of the OHP content that he or she is talking about.
The students can pay attention to that part of the OHP content which the lecturer is talking about, only if the part of the OHP content is pointed while the OHP content is being displayed in synchronism with the moving picture. To achieve this, the pointer position that the lecturer designates at the OHP must be detected in the moving picture (i.e., video-frame image) during the process of preparing the above-mentioned content.
The following are known as apparatuses for detecting the pointer position:
(1) Apparatus that Uses a Pointer Stick:
    (a) Method in which a pointer stick is used, and the image of the stick and the shade of the stick, both photographed with a vide camera, are extracted to determine the pointing position (see, for example, Patent Document 1)    (b) Method in which a light-emitting pointer stick is used and a light beam of a specific wavelength is extracted to determine the pointing position (see, for example, Patent Document 2)(2) Apparatus that Uses a Laser Pointer:    (a) Method in which a laser pointer is used, and each video frame is synchronized with the blinking of the laser beam to determine the image-projected area and the pointing position (see, for example Patent Document 3)    (b) Method in which a laser pointer is used, and a device that renders the projected image exactly as large as the photographed image is employed to determine the pointing position from the difference between the projected image and the photographed image (see, for example, Patent Document 4)    (c) Method in which a laser pointer is used, and a device that renders the projected image exactly as large as the photographed image is employed to determine the coordinates of the pointing marker on the screen from a light beam of a specific wavelength, from the blinking of a specific cycle, from a particular polarized light beam or from the difference between the projected image and the photographed image (see, for example, Patent Document 5)    (d) Method in which a laser pointer is used, an infrared-ray pointer is used to point the reference marker and pointing marker, both on the screen, and the positions of these markers are determined via an infrared-ray filter, thereby to determine the coordinates of the pointing marker (see, for example, Patent Document 6).[Patent Document 1]
Jpn. Pat. Appln. Publication No. 8-320921
[Patent Document 2]
Jpn. Pat. Appln. Publication No. 10-83246
[Patent Document 3]
Jpn. Pat. Appln. Publication No. 8-331667
[Patent Document 4]
Jpn. Pat. Appln. Publication No. 9-62444
[Patent Document 5]
Jpn. Pat. Appln. Publication No. 9-80372
[Patent Document 6]
Jpn. Pat. Appln. Publication No. 11-85395
The method (1) that uses a pointer stick is disadvantageous in that the lecturer can hardly deliver a good lecture. Since the lecturer uses the stick, his or her face turns. This does not meet the requirement that the lecturer's face be photographed in close-up mode in the content.
The method (2) that uses a laser pointer requires high cost, for the following reasons.
In the method (a), there must be used a special laser pointer that blinks in synchronism with video frames and a special device that capture the blinking cycle of the laser pointer and video images at the same time.
In the method (b), it is necessary to use a special device for performing video projection and the video photographing at the same time and a device for rendering the projected image exactly as large as the photographed image.
In the method (c), a device for rendering the projected image exactly as large as the photographed image must be used as in the method (b).
In the method (d), a reference marker and a pointing marker must be displayed on the screen by applying an infrared ray. The method (d) therefore requires a special laser pointer and a special projector.
In the conventional technique of detecting a pointer position:    (1) Special devices and a special environment required in order to detect a laser-pointer position from the video image of the laser pointer;    (2) A special device must be used to detect the pointer position from the image projected by a projector and to convert the pointer position to the coordinates in the source content or associate the pointer position with the coordinates.    (3) The projected image must be photographed in its entirety, always within the camera frame (or a device for photographing the image in this manner must be used). Therefore, the projected image cannot be zoomed in, and the camera cannot be moved up or down, or from the left to the right or vice versa to photograph only a part of the projected image.